Remove librtkaio support.
    
    The principal purpose of this change is to remove librtkaio support.
    
    The Fedora system wide change request is here:
    https://fedoraproject.org/wiki/Changes/GLIBC223_librtkaio_removal
    
    - Build require gcc-c++ for the C++ tests.
    - Support --without testsuite option to disable testing after build.
    - Support --without benchtests option to disable microbenchmarks.
    - Update --with bootstrap to disable benchtests, valgrind, documentation,
      selinux, and nss-crypt during bootstrap.
    - Support --without werror to disable building with -Werror.
    - Support --without docs to disable build requirement on texinfo.
    - Support --without valgrind to disable testing with valgrind.
    - Remove c_stubs add-on and enable fuller support for static binaries.
    - Remove librtkaio support (#1227855).